1. Field of the Invention
This invention relates to container closures and more particularly to such closures having an integral structure which makes a gas and moisture tight seal with the container wall.
2. Background Information
There are packaging applications, such as for example, in the food packaging industry and the craft supplies industry, which have a requirement for a cap which performs acceptably under certain oxygen transmission and moisture evaporation tests. Oxygen contamination or moisture evaporation can spoil the contents of a package not properly sealed to preclude this type of seepage. An example of an oxygen sensitive product is mayonnaise which will spoil over time with oxygen penetration. An example of a product affected by moisture evaporation is a water based craft paint which can dry out before use if the container is not adequately sealed. Another packaging application where there has been difficulty in effecting adequate sealing is plastic containers for carbonated beverages.
Currently metal or plastic caps with internal soft liner seals are used to reduce seepage to an acceptable level or to eliminate oxygen contamination. In addition, various linerless seals have been proposed. Many of these have annular flanges which bear against or fold over the rim of the container. Some form plug seals. These linerless seals are not as effective as the soft liner seals, however, they can be integrally molded with the closure and therefore are less expensive to produce.
We have found that a major detriment to effecting an adequate seal against seepage and oxygen contamination is damage on the container sealing surfaces in the form of scratches and other blemishes caused by tooling or handling equipment.
It is a primary object of the present invention to provide a closure having an effective seal against oxygen contamination and moisture seepage even for containers having scratches or other blemishes on the sealing surfaces and which does not require a soft liner.